Potty Training hell

Right now, I am almost a year into potty training and it has become pointless. My youngest child is almost 3 and should be using the potty all the time. He apparently only does so when he feels like it.
For instance on a long car ride. He doesn't like to sit in a yucky diaper; so miraculously he can hold it and uses the potty every stop we make over the course of a 17 hour drive.

 Unfortunately when we are at home he could care less. When he is at MOPS and Mommy's morning out he is using the bathroom. All the workers are so amazed that he is potty trained. I am also amazed and annoyed.

So with that said, I know I have successfully taught him to go potty, because he does it so well when he wants to. Now if I could just get him to go potty for me. I am so tired of buying diapers and carrying a diaper bag. The other day I caught myself day dreaming about burning the diaper bag in our fire pit!!

Tips anyone??